Scabies or sarcoptic mange, which is caused by infection with the parasitic mite Sarcoptes scabiei, is a widespread, highly contagious disease. The parasite has been found in well over 40 different mammals, including man. During the infection, female mites burrow in the skin to feed and their activities cause an intense irritation that leads to itching and scratching, which may aggravate the condition. Sensitization of the host to the mites and their products probably plays an important role in the pathogenesis of the disease. In its extreme form, scabies can develop into a severe hyperkeratotic form, where several thousands of mites can be found in the lesions. This form of crusted scabbies is also frequently observed among immune compromised individuals, i.e. HIV patients.
The standard method for diagnosing scabies include microscopic detection of the mites and their eggs and feces in skin scrapings. This method is relatively time-consuming and, in many cases, the results of microscopic examination can be negative owing to the low number of parasites present in each sample. The use of enzyme-linked immunosorbent assays (ELISA) for the detection of antibodies to S. scabiei has been reported for several different animals including humans (Bornstein & Zakrisson (1993) Vet. Dermatol. 4:107; Arlian et al. (1994) Exp. Parasitol. 78:37; Normaznah et al. (1996) Southeast Asian J. Trop. Med. Public Health 27:53; and Hollanders et al. (1997) Vet. Parasitol. 69:117). The ELISA technology offers several distinct advantages compared to skin scrapings: A relative ease of sampling, the potential to screen large numbers of samples and the possibility to standardize reagents and methods. The only major drawback is the limited amount of antigenic material available due to the lack of an in vitro propagation system for S. scabiei. 
Arlian and colleagues (J. Med. Entomol. (1988) 25:52) have developed an in vivo propagation system after establishing S. scabiei var. canis on rabbits. However, the parasite burden is still relatively low and the method cannot be applied for the production of antigens for large scale screening projects. Mites from naturally infected red foxes have been successfully isolated in large numbers and used in ELISAs both for dogs and pigs. The difficulties involved in using wild foxes as a source for antigen supply are however evident.
This lack of material has not only limited large scale screening efforts and control programs among farm animals, but it has also limited the possibilities to study other aspects of scabies, for instance pathogenesis.
EP 0 473 111 provides a recombinant mite allergen which is effective as a therapeutic agent and diagnostic reagent for mite allergic diseases. However, the mite allergen of this reference are derived from a house dust mite, more specifically from Dermatophagoides farinae. Thus, firstly, the said house dust mite is found free-living in a house-hold environment and does not live as a parasite on a host. Thus, disease thereof is not the result of an infection but the inhalation of mites or mite body fragments or faeces. The inhalation of house dust mites may cause allergic reactions in susceptible individuals resulting in respiratory distress, such as asthma and rhinitis. Accordingly, EP 0 473 111 relates to molecules useful in the diagnosis and prevention of such conditions.